A formaldehyde-free bio-composite sheet used as adhesive with excellent water-wet bonding performance

Formaldehyde-free liquid adhesives derived from biomass are attractive candidates to petroleum-based counterparts. However, developing solid bio-adhesive with excellent wet strength and bonding performances remains a lasting challenge. Here, we report a bio-composite sheet consisting of soybean flour, paper, and cross-linking agent (Polyamidoamine-epichlorohydrin, PAE), and its wet strength and bonding performances was evaluated by paper straw and plywood application. The covalent crosslinking by the reaction of soybean protein and PAE plays a major role in the enhancement of various properties of the cured bio-composite sheet. The tensile stress of cured bio-composite sheet was only lower than the prototype sample 14.5% after 100 ℃ water soaking treatment for 2 h. Paper straw rolled from the bio-composite sheet displayed boiling water stable at the same condition, while had better flexural strength and natural degradability than the plastic straw. Bonding strength of plywood boned with bio-composite sheet reached 1.38 MPa, which was exceeded 97.1% than the requirement of the Chinese National Standard GB/T 9846–2015 for interior plywood. Given the simple and general strategy, the products based on bio-composite sheet can potentially be a new approach on the use of biomass adhesives, which also be a suitable solution to solve the environmental challenges (e.g., formaldehyde) in the field of biomass-based composites.